1. Field of the Invention
The present invention relates to a sheet post-processing apparatus, which takes in sheets, binds the sheets into a sheaf, and staples the sheaf of sheets.
2. Description of the Related Art
There is a conventional sheet post-processing apparatus, which takes in a sheet printed and ejected from a multi function peripheral (MFP), and performs post-processing based on the information output from the MFP. The sheet post-processing apparatus described in Japanese Patent No. 2906046 aligns sheaves of sheets supplied to a processing tray, and staples the sheaves of sheets at two positions at the edge of the side of each sheaf. When the sheet post-processing apparatus staples a sheaf at a first position and then at a second position, the sheet post-processing apparatus holds the area of the sheaf between the first and second stapling positions by a pressing means, thereby preventing swelling of the sheaf at two stapling positions.
A stapler incorporated in the sheet post-processing apparatus has a sheaf inserting port which has a gap for clipping the sheaf larger than the thickness of the sheaf. When a sheaf of sheets is stapled, a sheaf is inserted into the port leaving a clearance for a staple. The stapler has a magazine loaded with staples, and an anvil to bend and shape the point of a staple that has pierced a sheaf of sheets.
Generally, one of the magazine and anvil is held, and the other is rotationally moved with respect to the fixed one. A sheaf of sheets is clamped, and a staple loaded in the magazine is shot. The anvil bends back and shapes the point of the pierced staple. A sheaf of sheets is held in the insertion port leaving a clearance either side of the port. Therefore, as one of the magazine or anvil is fixed, a sheaf of sheets is bent toward the fixed part when the sheaf is clamped. Considering that the number of sheaves varies randomly, a processing tray, on which sheets are stacked, is often used as a fixed and supported side.
Therefore, when a stapler clamps a sheaf of sheets, the sheaf is pressed to the fixed part of the processing tray side by the movable part, and is bent along the edge of the processing tray. An air layer is formed among sheets, and if the number of sheets to be bound into one sheaf is large, a sheet may be displaced during stapling, and may not be normally pierced by a staple of the stapler.
To solve the above problem, the edge of the processing tray is distant from the stapler, so that the whole sheaf of sheets can easily be bent to meet the movement of the stapler. A clearance from the processing tray to the stapler is filled by sticking a separately prepared film-like member.
However, the film-like member must be manually attached to the processing tray, therefore the manufacturing cost of the post-sheet processing apparatus is increased. Further, even if the film-like member is stuck well, a sheet warps a little after printing, and may run into the clearance between the film member and the processing tray, causing a jam.